Question

The code works fine in iOS5+:

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"FooBar"];
request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"ident"
                                                                                 ascending:NO
                                                                                  selector:@selector(compare:)]];
request.predicate = [NSPredicate predicateWithFormat:@"xxx = %@", @"yyy"];

self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                    managedObjectContext:model.managedObjectContext
                                                                      sectionNameKeyPath:nil
                                                                               cacheName:nil];

But in iOS 4, I got the following error:

'NSObjectInaccessibleException', reason: 'This fetch request (0x70d4700) 
was created with a string name (FooBar), and cannot respond to -entity 
until used by an NSManagedObjectContext'

2012-11-08 12:12:18.093 hello[1566:11d03] *** Terminating app due to uncaught
exception 'NSObjectInaccessibleException', reason: 'This fetch request 
(0x70d4700) was created with a string name (FooBar), and cannot respond 
to -entity until used by an NSManagedObjectContext'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x012405a9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x0104a313 objc_exception_throw + 44
    2   CoreData                            0x000be68f -[NSFetchRequest entity] + 159
    3   CoreData                            0x0019f7fb -[NSFetchedResultsController initWithFetchRequest:managedObjectContext:sectionNameKeyPath:cacheName:] + 763
    ...

How can I resolve this error?

Answer 1

fetchRequestWithEntityName: is available only in iOS 5 and later.

On iOS 4, you have to create a NSEntityDescription first:

NSEntityDescription *fooBarEntity = [NSEntityDescription entityForName:@"FooBar" inManagedObjectContext:model.managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:fooBarEntity];